On the Question of Terminology in the Field of Inclined Layers

D. A. Strelnikov

Under the conditions of the Kuzbass, when during the period of the Soviet five-year plans the task arose of choosing a system for working coal seams of especially 4–5–6 m thickness with gentle or inclined dip, attention was more often focused on one of the standard layer systems of working for thick seams, when the seam was artificially divided into two inclined layers separated from one another by a surface parallel to the bedding planes of the given coal seam being worked—its roof and floor. Usually these inclined layers were worked in descending order and with caving.

This was so until, in the years of the Soviet five-year plans, work on the development of the coal wealth of the “pearl of Kuzbass”—the Prokopyevsk-Kiselevsk district—with its often thick steeply dipping seams, in a number of cases with the presence of partings, became widely deployed. The presence of the latter justified to an even greater degree the use of inclined layers, when the partings were used as a roof or floor, created by nature itself, for the separated inclined layers. The steep dip of the seams being worked made it necessary to use stowing in the mined-out space, but the stowing material, which was then obtained and is still obtained at the outcrops of the seams being worked and in special quarries, was loose, friable, and poorly consolidated even over a long period of time; moreover, the number of layers in the seams being worked was most often no more than three.

Such conditions of occurrence of the coal seams led the engineering and technical workers of the Prokopyevsk district to the decision to carry out extraction by inclined layers not in descending, but in ascending order.

Thus, even in the years before the Great Patriotic War, variants of inclined layers were created and applied in Kuzbass, primarily with extraction in descending and ascending order, with caving and with stowing (Fig. 1).

Under the conditions of the Prokopyevsk-Kiselevsk district, working by inclined layers with stowing was carried out, and is now carried out, only in ascending order. If it proves possible to bring experiments with cementation of local stowing materials to industrial adoption, then the possibility and expediency cannot be excluded of switching in this district of Kuzbass to extraction of inclined layers on steep seams in descending order, which, as is known, has a number of positive aspects. Moreover, the experience of working steeply dipping coal seams in the Chelyabinsk district with relatively rapidly consolidating stowing materials confirms the possibility of applying inclined layers with stowing and extracting them in descending order.

The use of inclined layers on steep seams differs very advantageously from the possible use, under the same conditions, of variants of horizontal layers in that, when inclined layers are used, it is simple and easy,

the gravity flow of the mined coal and the placing, in its stead, of stowing materials into the worked-out space are also carried out. At the same time, however, the use in the Prokop’evsk mine of inclined layers, even with complete stowing on steep seams with a dip especially greater than 60°, did not guarantee mining operations that were sufficiently safe. This compelled the engineering and technical workers of Kuzbass—innovators—to seek additional modifications of the new variants of inclined layers that would make it possible to render mining operations safer.

Fig. 1.
“Properly speaking, inclined layers,” with extraction of layers in descending order (1, 2, 3), with caving—A, and in ascending order (I, II, III), with stowing—B. Both sections are across the strike of the seams.

These searches led first to the proposal of diagonal layers, later the so-called “herringbones” and “half-herringbones,” transverse-inclined layers, etc.

In all these searches the following is characteristic:

1) the imparting to artificially created layers of an inclined dip of up to 40–50°, when gravity flow of the coal and of the stowing is ensured; and

2) extraction of the layers in ascending order and with stowing.

The diagonal layers shown in schematic Fig. 2 in the form of a vertical section along the strike of the seam can be regarded only as a variant of inclined layers extracted in ascending order, which, with their dip angle of 40–50°, made possible the use of the simplest, cheapest type of gravity stowing. But experience in the use of diagonal layers with gravity stowing revealed a number of major shortcomings inherent in them:

1) great settlement of the stowing, 2) unreliable support of the stoping faces, 3) what is especially important, delamination of the “immediate roof,” 4) large coal losses, 5) difficulty of retaining, in the upper part of the stoping faces, the “side” coal wedge, 6) a comparatively short front of stoping operations, 7) low productivity of the extraction sections, and 8) low labor productivity of the miners in the section.

As a result of the establishment of the existence of these shortcomings, diagonal layers, which had seemed suitable for wide use in the working of steeply dipping coal seams, soon ceased to be used altogether.

As a result of further searches, experience was gained in the use, instead of diagonal layers, of a variant proposed by mining engineer, now Candidate of Technical Sciences, V. F. Parusimov: the “herringbone” (Fig. 3). These are the same diagonal (or, more precisely, inclined) layers with a distinctive so-called double-pitched stoping face. It was assumed that, under such conditions of working thick seams, operations could be organized so that when coal extraction is being carried out in one stoping face (“slope”), stowing is being carried out at the same time in another; later the crews working in these

“ramps,” change places, and in this way both crews had a constant, sufficiently broad working face. In this variant, the gravity flow of coal and stowing material was preserved. By shortening the length of the extraction section along the strike of the seam, the aim was to ensure more rapid extraction

Fig. 2.
Diagonal slices with their extraction in ascending order, with stowing. Section along the strike of the seam.

of coal in the extraction section. Nevertheless, in this variant it was not possible to eliminate cases of lagging of the “roof strata,” and with them collapses, considerable losses of coal, and, moreover, roof control. In addition, the cleavage of the coal seams of the Prokop’evsk district did not always prove usable for facilitating coal extraction; often it even contributed to the “falling out” of large lumps and slabs of coal from the “roof.”

Fig. 3.
Diagonal slices with a two-ramp face—“fir tree.” Section along the strike of the seam.

The last shortcoming of the “herringbone” variant revealed by practice led engineer P. M. Kovachevich to put forward yet another modified variant of diagonal layers, or, more precisely, also a variant of typical inclined layers, with a single-slope face (Fig. 4). Here again, in this variant, we have separate, relatively short extraction sections along the strike of the seam being worked (“pillars”). The author of this proposal believed that, when this variant was applied, the work of extracting coal and producing stowing would be carried out simultaneously in two adjacent pillar sections: in one—coal extraction; in the other, at the same time—stowing; later, the crew working on coal extraction moves into the pillar where stowing had previously been carried out, while the crew from that section moves into the section where coal extraction had been carried out and where stowing must now be performed.

Fig. 4.

Diagonal layers with a single-slope face—“half-herringbone.”
Section along the strike of the seam.

This variant, too, subsequently found no application in practice, since it did not promise to eliminate completely the shortcomings characteristic of diagonal layers.

Let us dwell on two more variants, also belonging to inclined layers (Figs. 5 and 6).

These variants were given the name transverse-inclined layers.

In both variants the layers occupy a position inclined to the horizon at an angle of up to 40–50° and dip crosswise (or transverse) to the strike; hence their name.

In Fig. 5 the transverse-inclined layers have the same direction of dip as the seam being worked, concordant with it, while in Fig. 6 the direction of dip of the transverse-inclined layers is opposite to the direction of dip of the seam being worked. Although the first variant has been tested in mines, it is hardly likely to find application in mines, particularly in the Prokopyevsk district of Kuzbass, since extracting coal in the layers both at the roof and at the floor of the seam is difficult. The second variant was at one time proposed by senior research associate of KuzNIIUI, Candidate of Technical Sciences B. M. Skoryi. At present this variant can be seen successfully applied at the I. V. Stalin mine of the Prokopyevsk mine group of Kuzbass. With this variant of inclined layers, many layers have been mined favorably in ascending order, with stowing. Both these va-

the variant are intended for use on steep coal seams with dip angles of not less than \(60^\circ\).

One cannot fail to note yet another proposal made by T. Ivanov in the years before the Great Patriotic War: to apply, on the thick steeply dipping seams of the Prokopyevsk-Kiselevsk district of Kuzbass, inclined layers arranged in the same way, coordinated with the direction of the cleavage planes on the individual seams of this district that is most favorable for coal extraction.

Fig. 5.

Transversely inclined layers with a dip consistent with the dip of the seam being worked. Cross-section across the strike of the seam.

This variant can hardly find application, since the presence of cleavage in the seams of the Prokopyevsk-Kiselevsk district, although established for a number of directions, can scarcely in practice be designed into a variant of an inclined-layer system with corresponding elements.

Fig. 6.

Transversely inclined layers with a dip of the layers opposite to the dip direction of the seam being worked. Cross-section across the strike of the seam.

layers, taking into account chiefly the direction of the cleavage planes and their position in space.

The data presented above indicate, first, the great initiative shown by the engineering and technical workers of the Kuzbass in seeking, during the years of the Stalin five-year plans, the best systems for working thick steeply dipping seams of the Kuzbass; second, that the variants advanced, partially tested, and now being used—as, for example, transverse-inclined layers—are all related to one of the standard systems for working thick coal seams: inclined layers.

It seems to us that, on the basis of the data and considerations set forth above, such working systems as diagonal layers and transverse-inclined layers, which are being proposed by individual authors for application and are now even being used at the I. V. Stalin mine in the Prokopyevsk mine field in the Kuzbass, should be regarded as nothing other than variants of inclined layers, and not as independent types of layered systems for working thick coal seams, a point that is often not taken into account in many publications and journal articles.

Thus, we propose that in textbooks, teaching aids, separate publications, and journal articles, the group of inclined layers used in working thick coal seams should include not only “inclined layers proper” (Fig. 1), where the surfaces dividing the layers are parallel to the bedding planes, that is, to the roof and floor of the seams, but also transverse-inclined layers (Fig. 6), used in the Prokopyevsk district of the Kuzbass, and diagonal layers (Fig. 2), which certain innovating authors propose to use at the present time as well, especially with the extraction of these layers in descending order.